Accurate clinical assessment of ligamentous stability of the knee is essential in cases involving joint disease or trauma to the knee. The present diagnostic technique involves applying unknown loads to the lower limb and observing the movements which occur. The objective of this project is to quantify ligamentous stability of the knee by accurate measurement of the load vs. displacement and moment vs. rotation relationships during the clinical examination procedure. Three tests will be performed: varus-valgus bending, tibial torsion and the anterior-posterior drawer test. Characteristic curves will be recorded on an x-ray plotter for four positions of knee flexion. A prototype apparatus for testing cadaver knees has demonstrated repeatability and reliability. Ligament sectioning studies will be performed on cadaver knees in order to measure changes in stiffness and laxity when specific ligaments or combinations of ligaments are cut. Tension tests on isolated ligaments will be performed. Stability characteristics of implanted total knee prostheses will be measured in cadaver knees; the effects of non-optimum prosthetic placement will be studied. A clinical testing apparatus will be developed to aid in diagnosing ligamentous disorders and to measure quantitatively the results of ligamentous repair and total knee replacement surgery. The stability data obtained from these studies will improve our understanding of the basic biomechanics of the knee joint and will allow us to establish the quantitative contribution of isolated ligamentous structures to the gross stability of the joint.